Surface-defect formation in graphite targets during magnetron sputtering

Abstract

Magnetron sputtering of graphite targets is frequently marred by the formation of topographic defects. The defects are either soft with a furry appearance or hard with a stalagmite appearance. The soft defects are often found on top of the hard ones, implying a close connection in formation sequence between the two types of defects. The formation mechanism of the hard defects is related to the presence on the surface of low sputtering-yield impurities or other types of lattice imperfections, which suppress the erosion induced locally by sputtering, and to porosity-induced asperities. The emergence of the soft defects is ascribed to a growth phenomenon involving redeposition of carbon from debris and possibly generated in a chemical vapor deposition (CVD) process. The gradual coverage of the target surface by defects causes a steady decrease of the sputtering rate of carbon. Also, the breakup of the soft defects promotes nodular defects in the subsequent growth of the carbon film, thus severely degrading the film quality. Remedial measures are devised for limiting the onset of defect formation.